Container cranes are used to handle freight containers and especially to transfer containers between transport modes at container terminals, freight harbours and the like. Standard shipping containers are used to transport a great and growing volume of freight around the world. Transshipment is a critical function in freight handling. Transshipment may occur at each point of transfer and there is usually a tremendous number of containers that must be unloaded, transferred to a temporary stack, and later loaded on to another ship, back onto the same ship or loaded instead onto another form of transport. Loading and unloading containers to and from a ship takes a great deal of time. The development of automated cranes has improved loading and unloading and made the productivity more predictable, and also eliminated many situations in which port workers have been exposed to danger and injury. Loading and unloading is seen as a bottleneck in terms of freight handling as the ships are idle in port while loading/unloading takes place. To reduce this idle time and container cranes are normally run continuously on long shifts until the loading or unloading of each ship is completed.
A container crane uses a number of powerful electric motors to power the moving parts and wind in or let out the wire ropes or cables used to lift a spreader holding a container up or down. Electric motors are used to power the movements of a trolley holding the spreader to lift and transport the containers out of the ship and onto a truck etc. on land, or vice versa if loading. Electrical power and control devices for operating the electrical motors of the crane, devices such as power converters, inverters, rectifiers, transformers and so on are placed in an electrical room. In use the electrical and electronic devices such as inverters, rectifiers and transformers develop significant quantities of heat as a consequence of electrical losses. For example, during normal operation in a crane electrical room the electrical and electronic apparatus generates from 1-30 kW per hour. This heat has to be removed from the electrical room to prevent equipment from running at too high a temperature and overheating. In electrical rooms for industrial plant and equipment generally it is common practice to cool the electrical rooms using a water supply in a heat exchanger to cool warm air from the electrical and electronic control and operating devices. This advantageous when there is a plentiful supply of clean and filtered fresh water. However, the electrical rooms for cranes and container cranes are usually cooled by air conditioners.
FIG. 5 (Prior Art) shows schematically a known type of cooling device for an electrical room, often called a split air conditioner. The figure shows an electrical room 15′ of a container crane which includes electrical and power electronic devices 16 which may be arranged with one or more local cooling fans 17. An inside air conditioner 21 including for example, one or more evaporator coils, is shown in the upper part of the room. The inside air conditioner is connected to an outside air conditioner 22, comprising for example, one or more condenser coils. Traditional cooling in this type of crane electrical room is carried out as follows. Outside air enters the electrical room through one or more lower inlets 12′. Warm air W generated by the thermal losses of the electrical and power electronic devices 16 rises, assisted by a fan included as part of the inside air conditioner 21. The warm air W is cooled by contact with evaporator coils or similar in an intake part of the inside air conditioner 21. The refrigerant or heat transfer fluid in the coils is circulated by pumps and/or compressors in the outside air conditioner 22. Heat extracted from the warm air in the electrical room is transferred to the outside air conditioner 22, also sometimes called an outdoor condenser unit, which transfers that heat further to the surrounding outside air. Some warm air may exit from the electrical room through upper ventilation openings 13. Cooler air C from an outlet part of the inside air conditioner 21 falls towards the floor of the electrical room 15′. In such a traditional cooling set-up the electrical room is commonly run with an inside temperature setpoint of 24° C. and it cools an average energy loss input of some 12.5 kW per hour using a power consumption of around 4.5-5.0 kW per hour.
The use of split air conditioners has several disadvantages. They are relatively inefficient, in part because the temperature differential between an inside temperature of 24° C. compared to an outside temperature may be small. In addition, most inside air conditioners tend to disrupt the natural convection flow of warm air rising to the ceiling then falling to the floor. This is because the inside air conditioner is positioned in the stream of warm air under the ceiling but direction of flow of cooled air pushed back by the inside air conditioner into the room is usually non-optimal and disturbs the natural convection flow. This is indicated schematically in FIG. 5 (Prior Art) as turbulent flow Wt in the warm air around the inside air conditioner. Perhaps as a consequence of the above inefficiencies, split air conditioners in any case tend to be run continuously at a higher speed, at least during daylight hours, in order to remove the heat generated by thermal losses in the electronic and electrical equipment, inverters, transformers, rectifiers and so on. The known indoor air conditioners and outside condenser units or outside air conditioners also consume a relatively great amount of electricity to cool the room. Standards introduced in recent years such as the Directive 2005/32/EC of the European Parliament of 6 Jul. 2005 established a framework for the setting of ecological design requirements for energy-using products. Such high levels of energy consumption are also in conflict with the intentions of other standards such as DIN 16001, a Management Standard for Energy Efficiency, and ISO 50001.
The inventors have noted that in the container crane industry, running split air conditioners at high loads continuously tends to result in a short service life of less than five years. In addition, continuous high loading results in unexpected breakdowns, which may disrupt production. The inventors therefore have endeavoured to provide an improved cooling device for electrical rooms in container cranes and other industrial applications with a similar service requirement. In addition, the common use of open loop air circulation introduces contaminants such as dirt, soot particles, pollen and moisture into the electrical room which can be deposited on surfaces of the electrical and electronic equipment. This causes a requirement for periodic maintenance and cleaning to avoid breakdown of insulating surfaces and burning of switch contact surfaces. As well, the moisture, soot and dirt particles are drawn into the indoor air conditioner by the fan which also leads to a reduction in thermal efficiency, leading in turn to overloading of the components of a split air conditioner.